A series of compounds with well defined and characterized responses to membrane potential will be developed. These compounds will bear chromophores which have been identified by molecular orbital theory calculations as being capable of displaying large linear electrochromic effects. The compounds will be prepared via flexible syntheses which will optimize favorable binding and orientation in membranes. The compounds will then be subjected to a battery of experiments to test their spectroscopic behavior in artificial environments. A hemispherical bilayer apparatus with phase locked detection will provide an indication of their response to applied electric fields. A series of experiments with phospholipid vesicles will test their binding, orientation, flipping mobility, and electrochromism in membranes. The probe response will thus be well understood and calibrated. Compounds which give positive results will be screened in a series of natural membranes. A squid axon model will be used to determine the fluorescent lifetimes of the compounds as a function of electric field during a nerve action potential. This system will also be used to detect voltage dependent changes in the intensities of transmitted and emitted light as a function of wavelength.